Cracking of hydrocarbons

ABSTRACT

A hydrocarbon cracking process and apparatus for recovering ethylene from hydrocarbon raw material streams. More particularly, the hydrocarbon cracking process and apparatus of this invention utilizes a furnace with a convection section and a radiant section in which the hydrocarbon feedstream is cracked by heating it to a particular temperature and then is self-quenched.

RELATED APPLICATIONS

[0001] This application claims the benefit of provisional application with the U.S. Serial No. 60/378,307, filed on May 7, 2002, which hereby is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a process and apparatus for cracking hydrocarbon feedstocks. More specifically, the invention is directed to a process and furnace in which a hydrocarbon is cracked by heating it to a particular temperature and then self-quenching itself within the furnace.

[0004] 2. Description of the Related Art

[0005] Thermal cracking of hydrocarbon feeds, which is also known as hydrocarbon pyrolysis, to produce olefins, diolefins and aromatics is a common petrochemical process. This process is frequently referred to as steam cracking since the hydrocarbon feeds are usually mixed with steam when they are heated to an incipient cracking temperature and cracked. Hydrocarbon feedstocks typically include, but are not limited to, ethane, propane, naphtha, or gas oil. The cracking takes place in a cracking furnace that typically comprises a radiant section, a convection section, and heat recovery equipment. In the convection or preheat section, a mixture of the hydrocarbon feed and steam are heated to an incipient cracking temperature, normally in the range of 1100° F. to 1300° F. The radiant, or cracking, section is where the cracking occurs. The heat recovery equipment recovers heat from the cracked hydrocarbons and the furnace flue gas.

[0006] The steam cracking process described above has been in commercial use for over sixty years and most of the current cracking furnaces are similar, even though differences exist depending upon the furnace designer. The hydrocarbons being cracked in the radiant section of the furnace pass through high alloy tubes that receive heat from the burning of natural gas and/or the less desirable light gasses produced in the furnace tubes. The tubes typically range from one to three inches in diameter and are forty to eighty feet in length. Some furnaces have a plurality of smaller tubes at the inlet of the radiant section joined to a smaller number of larger tubes, up to eight inches in diameter, at the outlet of the radiant section of the furnace. The tubes in the radiant section of the furnace exit the radiant section and then pass into exchangers, which cool and quench the furnace effluent to stop the cracking reactions taking place within the tubes.

[0007] Much has been learned about the desirable characteristics of the crucial radiant section of these furnaces that effect the yield of desirable olefins and diolefins produced from any hydrocarbon feed. Namely, it has been learned that the yield of desirable olefins and diolefins is increased when the partial pressure of hydrocarbons in the radiant section of the furnaces is decreased. It has also been learned that yield of desirable olefins and diolefins is increased when the effective residence time, during which time the cracking occurs, is reduced.

[0008] As a result of this knowledge, recently installed cracking furnaces have residence times in the radiant sections of from 0.1 to 0.3 seconds. The furnace effluent is then quenched as soon as possible after leaving the radiant section of the furnace. The typical residence time between exiting the furnace and being quenched is between 0.01 to 0.04 seconds, which has a detrimental effect on the yield of the desirable olefins and diolefins.

[0009] In one representative example of a known hydrocarbon cracking furnace, there is a convection section and a radiant section. The radiant section is cubed shaped and contains only vertical radiant tubes that are between 1″ and 4″ in diameter. The radiant tubes can have internal fins, but they are not required. The cracking residence time for this furnace is 0.07 seconds to 0.2 seconds. However, weaknesses exist in this design. Even though the residence times are short, there is still a potential for coking within this residence time range. Additionally, this furnace relies on external cooling to quench the cracking reaction once the effluent stream has left the furnace. The requirement for an external heat exchanger increases energy costs and capital costs.

[0010] To prevent coking within cracking furnaces, others have attempted to chemically halt coking by the addition of decoking fluids or by making process changes to their hydrocarbon cracking process. In one proposed process, a decoking fluid is injected into the hydrocarbon feedstock to prevent coking. In addition, the cracking temperature is lowered to 1550° F. to 1850° F. and uses a residence time of 0.01 to 0.10 seconds. While the coke formation may be decreased, this process requires the addition of expensive chemicals to prevent decoking and has decreased efficiencies since lower cracking temperatures are used. Additionally, in order to cool and stop the cracking process, additional heat exchangers are required.

[0011] Most furnaces operate at low discharge pressures ranges of four to fifteen psig. However, there is a considerable pressure drop in the radiant section due to coking that is detrimental to the yields of desirable products. When the partial pressure of hydrocarbons increases, then the yield of desirable products decreases.

[0012] A need exists for a hydrocarbon cracking process and furnace that will increase the yield of desirable products, decrease coke formation within the furnace, decrease the residence times within the cracking process, and provide potential cost saving benefits such as lower capital costs, lower energy consumption, and lower pressure ratings for equipment.

SUMMARY OF THE INVENTION

[0013] Typically in hydrocarbon cracking processes, the stream to be cracked is heated such that the bulk temperature of the stream is substantially higher than the incipient cracking temperature of the hydrocarbon being cracked. Cracking occurs in this bulk stream. In this invention the bulk stream to be cracked is heated to below the incipient cracking temperature but is passed through a very hot tube such that the boundary layer between the bulk fluid and the hot tube is heated to a sufficiently high temperature to cause cracking to take place only in the boundary layer. This results in the reaction being self quenching as the molecules pass back and forth between the hot boundary layer and the cool bulk fluid, which is at a temperature below incipient cracking temperature. Mixing is needed to enhance the transfer of the molecules between the bulk fluid and the boundary layer. Mixing is ideally performed by utilizing internals fins within the furnace tubes in which the cracking process occurs. Since cracking only occurs in the boundary layer the cracking residence time is substantially lower than with current technology and therefore the yields of the most desirable products are greatly enhanced.

[0014] In addition to the new hydrocarbon cracking process, a new furnace has been developed to optimize the new hydrocarbon cracking process. The new furnace is designed to operate at the higher tube metal temperatures, with lower residence times, required for this process. The new furnace has at least two sections, but can have more. The first section, or convection section, is for preheating the hydrocarbon feedstock fed to the furnace. The second section, or radiant section, is where the cracking process occurs. Within the radiant section is a plurality of furnace, or radiant, tubes. As opposed to most furnaces, the radiant tubes within the present furnace are much shorter and typically have smaller diameters than previous models. The radiant tubes also have internal fins internally mounted within to assist in the transferring of molecules between the bulk fluid layer and the boundary layer.

BRIEF DESCRIPTION OF THE DRAWING

[0015] So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, may be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and is therefore not to be considered limiting of the invention's scope as it may admit to other equally effective embodiments.

[0016]FIG. 1 is a simplified process flow diagram of the improved hydrocarbon cracking process in accordance to the present invention;

[0017]FIG. 2 is a partial cross-sectional view of a furnace for hydrocarbon cracking hydrocarbon feedstocks in accordance with the process in FIG. 1;

[0018]FIG. 3 is a cross-sectional view of a furnace for hydrocarbon cracking hydrocarbon feedstocks in accordance with the process in FIG. 1, taken along the line 3-3 of FIG. 2; and

[0019]FIG. 4 is a partial cross-sectional view of a radiant tube with internal fins in accordance with the apparatus of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0020] This invention is directed to a process and apparatus 10 for cracking a hydrocarbon feedstock 12 to recover olefins, diolefins, and aromatics from a feedstock 12. The apparatus 10 is typically called a furnace. It shall be noted that any type of furnace vessel 50 could be utilized, including, but not limited to, a heater, boiler, kiln, kettle, or cracker.

[0021] The hydrocarbon cracking process begins by supplying a hydrocarbon feedstock 12 to the furnace 50. The furnace 50 has at least two sections. The first section 14 is typically called a convection section or a preheat section. Many times, steam 16 is added to the hydrocarbon feedstock 12 prior to entering the furnace 50 or prior to preheating the feedstock 12, either of which would be considered as adding steam 16 to the hydrocarbon feedstock 12 while it is being supplied to the furnace 50. All embodiments of the present invention are believed to work, whether or not steam 16 has been added to the hydrocarbon feedstock 12. In the convection section 14 of the furnace 50, the hydrocarbon feedstock 12 is preheated to a temperature in the range of about 500° F. to about 900° F., or more preferably in the range of about 600° F. to about 800° F. The manner in which the feedstock 12 is preheated will be apparent and is also known to one skilled in the art.

[0022] Once the hydrocarbon feedstock 12 has been preheated, the feedstock 12 is transferred to the second section 18 of the furnace 50. The second section 18 is typically called a radiant section, a cracking section, or a fired section of the furnace 50. The second section, or radiant section, 18 typically contains a plurality of radiant tubes 20 through which the preheated hydrocarbon feedstock 12 travels, as shown in FIGS. 2 and 3. The second section 18 also contains a plurality of burners 22 that supply the heat that is necessary for cracking the preheated hydrocarbon feedstock 12 contained within the radiant tubes 20. Natural gas or the lighter undesired cracked gasses are typically used as fuel gas, but any suitable alternate can be used.

[0023] The radiant tubes 20 are typically constructed of a high alloy material to enable the tubes 20 to withstand the severe conditions within the furnace 50. However, any material suitable for this type of process is a suitable substitution, provided it has the requisite strength and durability to function within a furnace and is compatible with the chemicals in the method. The tubes 20 have a length in the range of about 4 feet to 12 feet or more preferably from about 5 feet to about 8 feet. The tube 20 diameters vary between about 0.5 inches to about 2.5 inches, or more preferably 0.75 inches to about 1.5 inches.

[0024] In a preferred embodiment of the invention, when the preheated hydrocarbon feedstock 12 is transferred to the radiant tubes 20 in the radiant section 18 of the furnace 50, a flow distributor 24 is installed at the inlet of each radiant tube 20, but external to the radiant section 18. The function of the flow distributor 24 is to evenly distribute the preheated hydrocarbon feedstock 12 flow to each of the radiant tubes 20. A venturi 25 is a suitable flow distributor 24 for this purpose. However, other devices or techniques that adequately perform the foregoing described function could, if desired, be used in the present method and apparatus, provided that they are constructed with materials that are compatible and the chemicals used in the present method and the severe conditions of the method.

[0025] The preheated hydrocarbon feedstock 12 is transferred to the tubes 20 in the radiant section 18 at a mass velocity of about 1 lb/sec/ft² to about 5 lb/sec/ft², or more preferably between about 2 lb/sec/ft² to about 4 lb/sec/ft². If steam 16 has been added to the hydrocarbon feedstock 18, the mass velocity remains the same.

[0026] The burners 22 within the radiant section 18 are those typically known in the art. The only requirement is that the burners 22 need to be able to supply enough heat to reach a tube metal temperature for the radiant tubes 20 in the range of about 2000° F. to about 2300° F., or more preferably between about 2100° F. and 2200° F.

[0027] Once the preheated hydrocarbon feedstock 12 is in the radiant section 18 of the furnace 50, the feedstock 12 is heated until the radiant tubes 20 have a tube metal temperature in the range of about 2000° F. to about 2300° F. The preferred range is between about 2100° F. and 2200° F. When the desired tube metal temperature is reached, at least some of the preheated hydrocarbon feedstock 12 is cracked, which produces a layer of cracked molecules within the tubes 20 called a boundary layer 24 (not shown). At least some of the remaining uncracked, or partially or lesser cracked, preheated hydrocarbon feedstock 12 remains in what is called a bulk fluid layer 26 (not shown), which is also within the same tubes 20 as the boundary layer 24. The bulk fluid layer 26 contains uncracked molecules. Within the radiant tubes 20, the cracked molecules in the boundary layer 24 and the uncracked molecules in the bulk fluid layer 26 are mixed together. To assist in the mixing, the use of internal fins 28 within the radiant tubes 20 is the preferred method of mixing the molecules in the two layers, as shown in FIG. 4.

[0028] In this situation, cracking of the preheated hydrocarbon feedstock 12 will only occur in the boundary layer 24 between the inner surface of the hot radiant tubes 20 and the bulk fluid 26 passing through the tube 20, which will be below the incipient cracking temperature of the feedstock 12. Some portion of feedstock 12 entering the radiant tube 20 will be in the boundary layer 24, which will be at temperatures well above incipient cracking temperature and thereby cause these molecules to crack.

[0029] Each tube 20 contains internal fins 28 that are about 0.05 inches to about 0.25 inches in height, or more preferably in the range of about 0.0625 to about 0.125 inches high. The fins 28 preferably have a spiral or circular configuration. However, it is believed that other fin configurations will work and should be included within the scope of this invention. The fins 28 are mounted internally within the tubes 20, as demonstrated in FIG. 4. The mounting space between each fin 28 tip, or pitch, is in the range of about 2 inches to about 10 inches, or more preferably about 3 inches to about 6 inches.

[0030] As a result of the mixing of the cracked and uncracked molecules, at least some of the cracked molecules in the boundary layer 24 are transferred into the bulk fluid layer 26, which substantially instantly self-quenches and halts further cracking in the cracked molecules. Substantially instantly is defined in the range of about 0.002 seconds to about 0.005 seconds. Since such short time periods are too difficult to accurately measure, for simplification, this time is considered to be substantially instantly. Substantially simultaneously, uncracked molecules in the bulk layer 26 are transferred into the boundary layer 24 and become cracked molecules. Substantially simultaneously is defined as being as quick as practically possible.

[0031] Once the cracking process occurs in the radiant tubes 20, all of the streams from radiant tubes 20 are combined and exit the furnace 50 at an exit temperature of less than about 1250° F. Upon exiting the furnace 50, the effluent stream 30 can then be cooled and heat recovered from the stream by conventional heat exchanger and recovery systems whereby olefins, diolefins, and aromatics are recovered. With proper control of temperatures of the tubes 20 and the cracked hydrocarbons 30 exiting the radiant section 18, it is believed that the proper conversion of the hydrocarbon feedstock 12 will be obtained.

[0032] Even though this new process cracks the hydrocarbon feedstock 12 at a temperature in the range of 2000° F. to 2300° F., coke formation is kept at a minimum. Increased temperatures usually cause more degradation to coke. However, the chance for coking is significantly reduced in the present invention since the residence times are so short when compared to other comparable hydrocarbon cracking furnaces. The residence times for the present invention range from 0.002 to 0.005 seconds, as opposed to the 0.01 to 0.04 second range of prior hydrocarbon cracking processes.

[0033] There are several advantages of the improved hydrocarbon cracking apparatus over the current designs. The first advantage is that the effective residence time for cracking, which is the time the hydrocarbon feedstock or partially cracked molecules spend above the incipient cracking temperature, will be between 0.002 and 0.005 seconds. Only the molecules in the boundary layer 24 will be above incipient cracking temperature. The lower residence time will result in enhanced yields of desirable products from the cracking furnace 50 when compared to conventional cracking furnaces. The lower residence time also decreases coke formation, as previously discussed.

[0034] Another advantage of the current invention is that when the furnace effluent stream 30 exits the radiant section 18 with the bulk fluid below the hydrocarbon feedstock incipient cracking temperature, it is believed that mixing will cause an instantaneous quenching and cessation of cracking of the preheated hydrocarbon feedstock. Heat can then be recovered from the cracked effluent in much simpler and lower cost processes. Currently, additional heat exchangers are required to quench and stop the cracking process. This change is a considerable capital cost savings since no heat exchanger equipment is needed to quench the cracked hydrocarbons and stop the cracking process. Additionally, lower pressure rated equipment can be used since the pressure of the hydrocarbons will be lower than in current processes, which also reduces capital costs.

[0035] In addition to the shorter residence times and lower discharge pressures from the furnace, the pressure drop through the radiant tubes and the heat recovery equipment will also be much lower than in other current cracking apparatus. The lower pressure drop increases the yield of desirable products compared to currently accepted cracking technology.

[0036] A further advantage of the new hydrocarbon cracking process is that the net energy required for this process is believed to be substantially lower than available alternate designs. Since the cracking is self-quenching, the lower net energy requirement is due to not having to cool the cracked hydrocarbon stream to stop the cracking process, which reduces the need for additional heat exchangers to quench the stream. Energy will be saved by removing the need for a heat exchanger to quench the reaction.

[0037] It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as obvious modifications and equivalents will be apparent to one skilled in the art. Accordingly, the invention is therefore to be limited only by the scope of the appended claims. 

What is claimed is:
 1. A process for thermally cracking a hydrocarbon feedstock, comprising the steps of: (a) supplying a hydrocarbon feedstock to a furnace having at least a first and a second section; (b) preheating the hydrocarbon feedstock, in the first section of the furnace, to produce a preheated hydrocarbon feedstock; (c) transferring the preheated hydrocarbon feedstock to the second section of the furnace; (d) heating the preheated hydrocarbon feedstock until at least some of the preheated hydrocarbon feedstock is cracked within a boundary layer at an inside surface of the second section of the furnace; (e) mixing the cracked molecules of the boundary layer and the uncracked molecules of the bulk fluid layer; (f) transferring at least some of the cracked molecules from the boundary layer into the bulk fluid layer and substantially instantly self-quenching and substantially halting further cracking in the cracked molecules and substantially simultaneously transferring at least some of the uncracked molecules from the bulk layer into the boundary layer and cracking at least some of the uncracked molecules as a result of the mixing of the cracked and uncracked molecules; and (g) removing substantially all the cracked and uncracked molecules from the furnace at an exit temperature of less than about 1250° F.
 2. The process of claim 1, including the step of: adding steam to the hydrocarbon feedstock while the hydrocarbon feedstock is being supplied to the furnace.
 3. The process of claim 1, wherein the preheated hydrocarbon feedstock is transferred to the second section of the furnace at a mass velocity of about 1 lb/sec/ft² to about 5 lb/sec/ft² of the preheated hydrocarbon feedstock.
 4. The process of claim 3, wherein the preheated hydrocarbon feedstock is transferred to the second section of the furnace at the mass velocity preferably in the range of about 2 lb/sec/ft² to about 4 lb/sec/ft².
 5. The process of claim 1, wherein the hydrocarbon feedstock is preheated to a temperature in the range of about 500° F. to about 900° F.
 6. The process of claim 5, wherein the hydrocarbon feedstock is preheated preferably to a temperature in the range of about 600° F. to about 800° F.
 7. The process of claim 1, wherein the preheated hydrocarbon feedstock is heated in the second section to a tube metal temperature in the range of about 2000° F. to about 2300° F.
 8. The process of claim 7, wherein the preheated hydrocarbon feedstock is heated in the second section to a tube metal temperature preferably in the range of about 2100° F. to about 2200° F.
 9. The process of claim 1, wherein the preheated hydrocarbon feedstock is transferred from the first section to the second section of the furnace by radiant tubes that have an internal diameter in the range of about 0.5 inches to about 2.5 inches.
 10. The process of claim 9, wherein the transferring of the preheated hydrocarbon feedstock to the second section of the furnace is by utilizing a flow distributor to evenly distribute flow to the radiant tubes.
 11. The process of claim 10, wherein the transferring of the preheated hydrocarbon feedstock to the second section of the furnace is by utilizing a venturi meter to evenly distribute flow to the radiant tubes.
 12. The process of claim 9, wherein the preheated hydrocarbon feedstock is transferred from the first section to the second section of the furnace by radiant tubes having an internal diameter preferably in the range of about 0.75 inches to about 1.5 inches.
 13. The process of claim 9, wherein the preheated hydrocarbon feedstock is transferred from the first section to the second section of the furnace by radiant tubes having a length in the range of about 4 feet to about 12 feet.
 14. The process of claim 13, wherein the preheated hydrocarbon feedstock is transferred from the first section to the second section of the furnace by radiant tubes having a length preferably in the range of about 6 feet to about 10 feet.
 15. The process of claim 1, wherein the cracked molecules in the boundary layer and the uncracked molecules in the bulk fluid layer are mixed by utilizing internal fins.
 16. The process of claim 15, wherein the cracked molecules in the boundary layer and the uncracked molecules in the bulk fluid layer are mixed by utilizing internal fins that are spiral or circular.
 17. The process of claim 15, wherein the cracked molecules in the boundary layer and the uncracked molecules in the bulk fluid layer are mixed by utilizing internal fins that have a height in the range of about 0.05 inches to about 0.25 inches.
 18. The process of claim 15, wherein the cracked molecules in the boundary layer and the uncracked molecules in the bulk fluid layer are mixed by utilizing internal fins that have a height preferably in the range of about 0.06 inches to about 0.125 inches.
 19. The process of claim 15, wherein the cracked molecules in the boundary layer and the uncracked molecules in the bulk fluid layer are mixed by utilizing internal fins that are mounted within the radiant tubes of claim 10 at a spacing between each internal fin of about 2 inches to about 10 inches.
 20. The process of claim 19, wherein the cracked molecules in the boundary layer and the uncracked molecules in the bulk fluid layer are mixed by utilizing internal fins that are mounted within the radiant tubes at a spacing between each internal fin preferably of about 3 inches to about 6 inches.
 21. The process of claim 1, wherein the cracked molecules in the boundary layer and the uncracked molecules in the bulk fluid layer are transferred, cracked, self-quenched, and halted within a residence time in the range of about 0.002 seconds to about 0.005 seconds.
 22. A process for thermally cracking a hydrocarbon feedstock, comprising the steps of: (a) supplying a hydrocarbon feedstock to a furnace having at least a first and a second section; (b) adding steam to the hydrocarbon feedstock (c) preheating the hydrocarbon feedstock, the preheating occurring in the first section of the furnace, to produce a preheated hydrocarbon feedstock; (d) heating the preheated hydrocarbon feedstock until at least some of the preheated hydrocarbon feedstock is cracked within a boundary layer at an inside surface of the second section of the furnace; (e) heating the preheated hydrocarbon feedstock, until at least some of the preheated hydrocarbon feedstock is cracked to produce a boundary layer, which includes cracked molecules of the preheated hydrocarbon feedstock, and a bulk fluid layer, which includes uncracked molecules of the preheated hydrocarbon feedstock; (f) mixing the cracked molecules from the boundary layer and the uncracked molecules from the bulk fluid layer; (g) transferring at least some of the cracked molecules from the boundary layer into the bulk fluid layer and substantially instantly self-quenching and substantially halting further cracking in the cracked molecules and substantially simultaneously transferring at least some of the uncracked molecules from the bulk layer into the boundary layer and cracking at least some of the uncracked molecules as a result of the mixing of the cracked and uncracked molecules; (h) removing substantially all the cracked and uncracked molecules from the furnace at an exit temperature of less than about 1250° F.; and (i) cooling and removing heat from the cracked and uncracked molecules from the furnace to recover olefins, diolefins, and aromatics from the hydrocarbon feedstock.
 23. A furnace for thermally cracking a hydrocarbon feedstock, comprising: (a) a first section for receiving and preheating the hydrocarbon feedstock to produce a preheated hydrocarbon feedstock; (b) a flow distributor adapted to transfer the preheated hydrocarbon feedstock to a second section of the furnace; (c) the second section for heating the preheated hydrocarbon feedstock until at least some of the preheated hydrocarbon feedstock is cracked within a boundary layer at an inside surface of the second section of the furnace; wherein the second section includes: (d) a mixer for mixing at least some of the cracked molecules in the boundary layer and at least some of the uncracked molecules in the bulk fluid layer; (e) a fluid distributor adapted to transfer at least some of the cracked molecules from the boundary layer into the bulk fluid layer and substantially simultaneously transfer at least some of the uncracked molecules from the bulk fluid layer into the boundary layer; and (f) a conduit for removing substantially all the cracked and uncracked molecules from the furnace at an exit temperature of less than about 1250° F.
 24. The furnace of claim 23, further including a connector for adding steam to the hydrocarbon feedstock prior to preheating the hydrocarbon feedstock.
 25. The furnace of claim 23, wherein the flow distributor transfers the preheated hydrocarbon feedstock at a mass velocity in the range of about 1 lb/sec/ft² to about 5 lb/sec/ft².
 26. The furnace of claim 23, wherein the flow distributor transfers the preheated hydrocarbon feedstock preferably at the mass velocity in the range of about 2 lb/sec/ft² to about 4 lb/sec/ft².
 27. The furnace of claim 23, wherein the first section preheats the hydrocarbon feedstock to a temperature in the range of about 500° F. to about 900° F.
 28. The furnace of claim 27, wherein the first section preheats the hydrocarbon feedstock to a temperature preferably in the range of about 600° F. to about 800° F.
 29. The furnace of claim 23, wherein the second section heats the preheated hydrocarbon feedstock to a metal temperature in the range of about 2000° F. to about 2300° F.
 30. The furnace of claim 29, wherein the second section heats the preheated hydrocarbon feedstock to the metal temperature preferably in the range of about 2100° F. to about 2200° F.
 31. The furnace of claim 23, wherein the fluid distributor includes radiant tubes that have an internal diameter in the range of about 0.5 inches to about 2.5 inches.
 32. The furnace of claim 31, wherein the radiant tubes have an internal diameter preferably in the range of about 0.75 inches to about 1.5 inches.
 33. The furnace of claim 31, wherein the flow distributor evenly distributes the preheated hydrocarbon feedstock to the radiant tubes in the second section of the furnace.
 34. The furnace of claim 31, wherein the flow distributor evenly distributes the preheated hydrocarbon feedstock to the radiant tubes in the second section of the furnace by utilizing a venturi meter.
 35. The furnace of claim 31, wherein the radiant tubes have a length in the range of about 4 feet to about 12 feet.
 36. The furnace of claim 35, wherein the radiant tubes have a length preferably in the range of about 6 feet to about 10 feet.
 37. The furnace of claim 23, wherein the mixer includes internal fins.
 38. The furnace of claim 37, wherein the internal fins are spiral or circular.
 39. The furnace of claim 38, wherein the internal fins have a height in the range of about 0.05 inches to about 0.25 inches.
 40. The furnace of claim 39, wherein the internal fins have a height preferably in the range of about 0.06 inches to about 0.125 inches.
 41. The furnace of claim 37, wherein the internal fins are mounted within the radiant tubes of claim 31 at a spacing between each internal fin in the range of about 2 inches to about 10 inches.
 42. The furnace of claim 41, wherein the internal fins are mounted within the radiant tubes at a spacing between each internal fin preferably in the range of about 3 inches to about 6 inches.
 43. The furnace of claim 23, wherein the fluid distributor transfers, cracks, self-quenches, and halts cracking within a residence time in the range of about 0.002 seconds to about 0.005 seconds. 